The present invention relates to an automatic deployment and retrieval tethering system. In particular, the present invention relates to a system for automatically winding and unwinding cable, for example, fiber optic or electrical cable or a combination of both, from a moving vehicle. The moving vehicle might be, for example, a remotely controlled robot.
The invention relates to a cable deployment and retrieval system for a moving object, for example a robot having a tether or umbilical cord. Some robots do not use radio control, for example, because of interference, and require an umbilical cord to be attached to the robot to transmit or receive information or data, for providing control and possibly power, if the robot does not include its own power source. The problem with such umbilical cords or tethers is deploying the cable so that the cable does not become tangled when the robot moves in different directions. The cable deployment system must be able to deploy the cable as the robot moves forward and retract the cable as it reverses. In addition, the system must be able to allow the robot to go around corners without placing excess tension on the cable and must allow the robot to turn, sometimes in very tight quarters, without snagging the cable. There may be situations where even though the robot is not moving forward or backward, the cable must either be retracted or deployed, depending upon the turn that the robot is making. Additionally, the robot must be able to drive over the cable without snagging the cable and while still allowing cable to be extended or retracted.
There have been various attempts in the prior art to provide cable deployment systems. However, all of the prior art devices, as far as applicant is aware, suffer from various drawbacks.
U.S. Pat. No. 4,736,826 to white et al. is exemplary of efforts made in the prior art. In that patent, the tethering system uses a cable feed drive motor that deploys and retrieves cable. The system is wholly dependent on receiving encoded signals originating from the direction of rotation of the drive wheels of the robot vehicle itself.
Because in the device of the White et al. reference the cable feed drive motor is dependent on wheel rotation, and not on actual vehicle movement, if there is any slippage between the wheels and the ground, so that the wheels spin or in trying to stop, slip, the signal that would be sent through the encoders to the cable reel motor would reflect the rotation or non-rotation of the wheels, but not the actual movement of the vehicle. This would cause an incorrect amount of cable to be deployed or retracted by the cable reel motor relative to the actual vehicle movement, resulting in damage to the cable or the robot.
Another disadvantage of the device of the White et al. reference relates to when a robot is pivoted around its own center point. For example, if the drive wheels in the White et al. device would rotate in opposite directions with the same rotational speed, the robot would basically pivot around its own center point, and the encoder signals coming from the opposite drive wheels would vector each other out, and no cable would exit from the vehicle. However, as the exit point of the cable is above the pivot wheel, which is at some radial distance away from the exampled pivot turning center of the robot, the cable would have to be deployed at the same circumferential speed as the pivoting robot's cable exit point. However, vectorially the drive wheel encoders would cancel each other out, the cable would not deploy and the cable already deployed would go into extreme tension and break, or stop the robot from pivoting.
Other systems are also known in the prior art for deploying cable from a moving vehicle. In some, tension is sensed in the deployed cable. However, these systems typically employ a dancer arm, tension control arm or tension rollers to sense the tension in the deployed cable. The problem with these systems is that they typically operate in only one direction. For example, U.S. Pat. No. 4,666,102 to Colbaugh et al., shows an apparatus for automatically dispensing and taking up a flexible communications cable such as an optical fiber which includes a motor driven reel which is mounted on a vehicle. The fiber passes through a pivotably mounted tension control arm whose angular position is detected to control the motor. Depending on the position of the tension control arm, the reel may be rotated in one direction to relieve fiber tension or it may be rotated in the opposite direction to take-up slack, or it may remain quiescent.
The problem with the device of the Colbaugh et al. reference is that if the mobile vehicle makes a pivot turn, for example, such that the instantaneous direction of cable exit is at an angle with respect to the tension control arm, the tension control arm cannot respond properly since it can only pivot along one axis. Such a system will result in increased tension in the cable which cannot, be detected properly by the tension control arm, with subsequent damage to the cable and/or vehicle.
In U.S. Pat. No. 4,583,700 to Tschurbanoff, a cable winding system for electrically powered mine vehicles is disclosed. This system utilizes a pivotable extension arm having guide rollers thereon. Again, as in the device of Colbaugh et al., this system is incapable of sensing tension in all directions and is only capable of substantially sensing the tension in a direction collinear with the extension arm.
U.S. Pat. No. 4,692,063 to Conti describes a system for measuring the tension in a cable during underground placement in for example, a furrow formed by a tractor deploying the cable. The system measures the pressure of a hydraulic fluid supplied to a capstan motor to determine the tension in the cable which can be monitored so that if the tension increases the tractor can be stopped. If the tension increases without exceeding a trip point, the tractor can be slowed down to reduce the tension in the cable. The system of the Conti reference is for use in a forward direction only (i.e. unwinding) and further, is incapable of sensing tension in a 360.degree. arc around a cable exit point. Furthermore, the system of that reference is designed for large tractor size cable laying devices and not for mobile vehicles such as robots which perform very complex tasks including pivoting about an axis, rapid changes of direction and forward and reverse motions.
Another example of a unidirectional cable unwinding system is shown in U.S. Pat. No. 4,744,696 to Vidler. This device utilizes a slack loop formed in the cable during paying out and the amount of the cable in the slack loop is monitored to determine the tension in the cable.